The goal of this research is to understand the mechanism by which the bubonic plague bacterium, Yersinia pestis, colonizes its vector, the flea. This proposal describes an experimental system in which the nematode Caenorhabditis elegans is a surrogate for the flea, which allows use of powerful model organism genetic methods. Y. pestis colonizes the flea digestive tract and physically blocks the insect from feeding, leading to transmission of plague to new hosts through flea bites. This process requires the bacterial genes known as hms. Y. pestis creates a visible biofilm on the surface of C. elegans, which also requires hms genes. The biofilm blocks feeding of the nematodes and impairs their growth, a physical effect similar to the feeding blockage that occurs in the digestive tracts of infected fleas. These observations suggest that Y. pestis blocks fleas with a biofilm. The nematode will be used to further understand this process in an easily manipulated laboratory system, and the results can then be investigated directly in flea-bacteria interactions. The impact on human health of these studies will be: 1) Identification and characterization, in bacteria or flea or both, of molecular targets for drugs that could reduce or eliminate plague in rodent flea populations and be used in response to bioweapon attacks with plague-carrying fleas. 2) Deeper understanding of how biofilms attach to living tissues, a process important in a wide variety of infectious diseases. 3) Identification of nematode surface components, with potential for translation to treatment of helminthic infections. The specific aims of this proposal are: 1) Determine the roles in biofilm formation of hms and other Yersinia genes. 2) Determine the polysaccharide content and structure of the biofilm and develop reagents for its detection. 3) Clone three C. elegans gene involved in biofilm adherence and determine the localization in the worm of the encoded proteins.